Sulphur corrosion in cracking



Oct 24, 1944 J. N. J. PERQUIN SULPHUR CRROSION IN CRACKING Filed March25, 1945 lnvzn'or: Johannes N. J. -Perqul'n Patented Oct. 24, 19442,361,149 SULPHUR CORROSION IN CRACKIN G Johannes N. Jacobus Perquin,

Teddington, England, assigner to Shell Development Company, SanFrancisco, Calif., a corporation of Delaware Application March 23, 1943,Serial No. 480,244

('Cl. 19e-1) 9 Claims.

, The present invention relates to a process for inhibiting corrosion.More particularly, it relates to a process for inhibiting the corrosionof metallic surfaces used in the construction of equipment whereinhydrocarbons containing hydrogen sulphide Contact said equipment atelevated temperatures.

It is well known that metallic surfaces such as furnace tubes corrodewhen they are contacted with hydrocarbons containing hydrogen sulphideat elevated temperatures, such as may occur, for example, in thecracking, reforming, etc. of hydrocarbons.

It is an object of the present invention to reduce corrosion of metallicsurfaces in cracking, reforming, and other thermal processings ofhydrocarbons. Another object is to reduce the corrosion of surfacescomposed of ferrous metals which are contacted at relatively hightemperatures with hydrocarbons containing hydrogen sulphide. A furtherobject is to prevent hydrocarbons containing HzS from contactingmetallic surfaces at critical corrodng temperatures which are describedbelow.

This invention isv based upon the discovery that hydrogen sulphide inhydrocarbon fractions such as are derived, for example, from petroleum,exhibits a maximum degree of corrosion of ferrous metal surfaces attemperatures ranging from about 300 to 425 C., with the highest degreeof corrosion at about 370 C. t

In processes in which it is desired to heat a hydrocarbon mixturecontaining HzS to temperatures above about 400 C., the method of thisinvention provides a mode for preventing hydrogen sulphide fromcontacting metallic surfaces at temperatures `Within this range ofmaximum corrosion and for times longenough to cause damage. To achievethis, the HzS-containing hydrocarbons are kept relatively cool, e. g.are heated to temperatures below this critical temperature range, andthen are admixed rapidly with hydrocarbons poor in hydrogen sulphidehaving a temperature substantially above the critical temperature rangeto produce a mixture having a temperature above the critical range. Inthis manner, the hydrogen sulphide is heated so rapidly through thedangerous zone that it has no chance to come in contact with metallicsurfaces for a time long enough to cause material corrosion.

The accompanying drawing is a flow diagram to illustrate the improvementof this invention, or it may be applied, for instance, to a crackingprocess. Referring to the drawing, a hydrogen sulphide-rich hydrocarbonfeed which it is desired to treat at an elevated temperature isintroduced into furnace I through valved line 2, line 3, valved line 4and lim 5, at a temperature not exceeding about 325 C. and preferablynot exceeding 300 C. This feed may, however, be preheated to just belowthese temperatures by passing through valved line 6, preheater I andvalved line 8, around valved line '4, to join line 5. The preheater 'Imay be heated in any suitable manner such, for example, by the flue gasfrom furnace I in its stack 9.

This hydrogen sulphide-rich feed upon introduction into furnace I israpidly mixed at the junction I3 with a hydrogen sulphide-poorhydrocarbon feed in such an amount and having such temperaturesubstantially in excess of 400 C. and preferably in excess of 425 C., soas to produce a mixture having a temperature above 400 C. and preferablyabove 425 C.-say, for example, a temperature of about 480 C. 'I'hishydrogen sulphide-poor feed may be introduced into furnace I throughvalved line I0 and line I I and pass through heater I2, wherein it isheated to a temperature substantially above 425 C. before reachingjunction I3 in said furnace.

Mixing at junction I3 must be rapid, and it is therefore desirable thatan effective mixing device be installed at this point. If the heating ofthe I-lzS-rich stream is very rapid, little or no corrosion will occurat junction I3. However, there is danger that some corrosion may occurat this onepoint, in which case it is desirable to use a metal, such ashigh chromium nickel steel, in the construction of this mixing devicewhich is relatively resistant at sulphide corrosion.

The resulting heated mixture may then further be heated in coil I4located in furnace I and withdrawn through `valved lines I5 and I 5 intoa suitable reactor I'I wherein the proper time for the desiredreaction-for whatever purpose it may be-is allowed to elapse. Theresidue of liquids and tars is withdrawn from the bottom of reactor I'Ithrough cooler IB and line I9 and the reacted vapors are withdrawn fromthe `top of the reactor I1 through lines 20 and 2I wherein they arequenched at junction 22 by a suitable quenching fluid introduced throughline 23 before passing on through line 24 to the fractionators and/ortreaters. Alternatively the reactor I1 may be bypassed through valvedline 25 directly to the quenching junction 22 with line 23. Also heaterI4 may be by-passed through valved line 26 and the heated fluid passingthrough this line may proceed through reactor I1 or through the bypass25 to the quenching junction 22.

The quenching fluid may consist of an inert cold gas, hydrocarbonliquid, Water or other inert liquid whereby the temperature of thesevapors is reduced instantaneously from above the critical temperaturerange to below about 325 C. and preferably below about 300 C.

In a special modification, the I-IzS rich feed may be introduced throughvalved line 21 into fractionator 28 (which may be a fractional disbeapplied to the treatment mixtures which it is desired to heat and whichmust be maintained for various lengths of time at elevated temperaturesin contact with a ferrous metallic surf ace, which hydrocarbon mixturescontain H28 in amounts sufficient to cause corrosion undertheseconditions. The HzS content of various hydrocarbon mixtures frompetroleum is known to range between Wide limits, occasionally being ashigh as 5% or even higher, although in general it is below about .5%.However, it is particularly applicable to the treatment of hydrocarbonsor mixtures thereof comprising components of relatively low boilingpoint, for example methane, ethane, propane, butane, isobutane, thepentanes, various gasoline distlllates and naphthas, etc., which arecommonly derived from petroleums containing appreciable quantities ofsulphun Processes in which such hydrocarbon mixtures are heated to abovethe critical corrosion temperatures com? prise thermal and catalyticcracking, reforming, high temperature alkylation, `isomerization,hydrogenation, hydroforming, hydroiining, isoforming, dehydrogenation,cyclization, etc.

By ferrous metal surfaces are meant those surfaces of any apparatus withwhich the hydrogen sulphide-containing hydrocarbons come in contact atelevated temperatures.

vary with the equipment under consideration but, in general, iron is theprincipal constituent, such as in steels of various hardness containingc arbon, and alloy steels containing molybdenum, chromium, nickel,aluminum, silicon, etc.

Since the rate of corrosion of equipment by hydrogen sulphide-containinghydrocarbons is a function of the concentration of hydrogen sulphide asWell as the temperature, itis impossible to `state precisely the maximumhydrogen sulphide content permissible in the HzS-poor feed. In generalthe lower its content the lower will be the rate of corrosion. Thereforeit can only be said that the hydrogen sulphide content of this HzS-poorfeed or fraction should not be greater than, or should be reduced to,the lowest practicable value. As a rule, it is desirable that the-HzScontent be below about .2% and preferably below about .05%.

Although the present invention has been particularly described withreference to reducing the corrosion of heating elements, it is evidentthat it can be equally well applied to the protection The chemicalcomposition of such apparatus and surfaces will from corrosion ofblowers, heat exchangers, conduits, valves, reaction chambers, and thelike; in short, any apparatus in which it is necessary to contactcorrosive hydrocarbon mixtures containing hydrogen sulphide at elevatedtemperatures.

The following example represents an actual embodiment of this invention.

Example A propane-propylene fraction containing about 3% by volum'ehydrogen sulphide was admixed with a naphtha having a temperature ofbetween about 10G-200 C. and the mixture was run through the tubes of areforming furnace for a period of about four months, after which thefurnace was shut down and the tubes were inspected. These tubes weremade of a 4% to 6% chromium and .5% molybdenum steel. It was found thatonly those tubes were corroded which during operation were attemperatures between about 300 and 425 C. and a maximum corrosion wasnoticed in tubes which were at a temperature of about370o C. Thecorrosion decreased the wall thickness of these tubes as much as 4 mm.Those tubes which were above the temperature .of 425 C. were found to besubstantially free from corrosion, as were those tubes at temperaturesbelow 300 C.

In a later run the propane-propylene fraction containing the hydrogensulphide was rapidly admixed with the naphtha after the naphtha had beenheated to a temperature of 480 C. whereby a mixture was produced whichhad a temperature of about 430 C. This mixture was then further heatedto a temperature of about 560 C. before being quenched. After about fourmonths of such operation the furnace was again shut down and the tubesinspected and substantially no corrosion had occurred in any of them.

I claim as my invention:

1. In a process for treating a hydrocarbon containing hydrogen sulphidein a concentration sufficient to cause thermal corrosion to ferrousmetals, wherein said hydrocarbon comes in contact with such a ferrousmetal at a temperature above 425 C., the improvement comprising thesteps of mixing an amount of said hydrocarbon having a temperature notexceeding 325 C. with an amount of a second hydrocarbon containinghydrogen sulphide in a concentration insufficient for thermal corrosionhaving a temperature substantially above 425 C., to produce a resultingmixture of hydrocarbons having a temperature substantially above 425 C.,and contacting said hydrocarbons at a temperature substantially above425 C. with said ferrous metal.

2. In a process for treating a hydrocarbon of f relatively high hydrogensulphide content at elevated temperature wherein said hydrocarbon comesin contact with a ferrous metal surface, the improvement comprising thesteps of mixing an amount of said hydrocarbon having a ternperature notexceeding 325 C. with an amount of a hydrocarbon of relatively lowhydrogen sulphide content having a temperature substantially above 425C., to produce a resulting mixture of hydrocarbons having a temperaturesubstantially above 425 C., and contacting said hydrocarbons at atemperature substantially above 425 C. With said ferrous metal surface.

3. The process of claim 2 wherein said process for treating is acracking process.

4. The process of claim 2 wherein the hydrogen sulphide content of thehydrocarbon of rela-l tively high hydrogen sulphide content is betweenabout .2% and 5% by volume.

5. The process of claim 2 wherein the hydrogen sulphide content tivelylow hydrogen sulphide content is less than about .2% by volume.

6. In a process for treating a hydrocarbon of relatively high hydrogensulphide content at elevated temperature wherein said hydrocarbon comesin contact with a ferrous metal surface, the improvement comprising thesteps of mixing an amount of said hydrocarbon having a temperature notexceeding 300 C. with an amount of a hydrocarbon of relatively lowhydrogen sulphide content having a temperature substantially above 425C., to produce a resulting mixture of hydrocarbons having a temperaturesubstantially above 425 C., and contacting said hydrocarbons at atemperature substantially above 425 C. With said ferrous metal surface.

'7. In a process for treating a hydrocarbon mixture containing hydrogensulphide at elevated temperatures wherein said hydrocarbons come incontact with a ferrous metal surface, the improvement comprisingseparating from said mixture a rst fraction relatively rich in hydrogensulphide and a second fraction relatively poor in hydrogen sulphide,mixing an amount of said rst fraction at a temperature not exceeding 325C. with an amount of said second hydrocarbon fraction at a temperaturesubstantially above of the hydrocarbon of relastantially above 425 425C., to produce a resulting mixture of hydrocarbons having a temperaturesubstantially in excess of 425 C., and contacting said hydrocarbons at atemperature substantially in excess of 425 C. with said ferrous metalsurface.

8. In a process for treating a hydrocarbon of relatively high hydrogensulphide content at an elevated temperature wherein said hydrocarboncomes in contact With a ferrous metal surface, the improvementcomprising preheating said hydrocarbon to a temperature not exceeding325 C., mixing said preheated hydrocarbon with an amount of hydrocarbonof relatively low hydrogen sulphide content having a temperature sub-C., to produce a resulting mixture of hydrocarbons having a temperaturesubstantially above 425 C. and contacting said hydrocarbons at atemperature substantially above 425 C. with said ferrous metal surface.

9. A process for preventing corrosion of ferrous metals when contactedwith hydrocarbons of relatively high hydrogen sulphide content atelevated temperatures comprising the steps of mixing an amount of saidhydrocarbons having a temperature not exceeding 325 C. with an amount ofhydrocarbons of relatively low hydrogen sulphide content having atemperature substantially above 425 C., to produce a resulting mixtureof hydrocarbons having a. temperature substantially above 425 C.

JOHANNES N. JACOBUS PERQUIN.

